Climate-cooling effect 'stronger than volcanoes' is looking solid

Could be time to massage those hot models again

Opinion A newly discovered mechanism for cooling the planet - potentially, according to its discoverers, more significant even than the well-known chilling effects of volcanic eruptions - has now been further investigated.

The mechanism in question is the action of difficult-to-study atmospheric molecules known as "Criegee intermediates", whose existence was first theorised in the 1950s by German chemist Rudolf Criegee but not confirmed until recent years by boffins using methods which have only lately become available.

Criegee intermediates act to produce extra sulphuric acid - a well-known and powerful atmospheric aerosol which causes additional clouds to form, which in turn cools the climate. This mechanism is seen in action after major volcanic eruptions, which hurl huge amounts of sulphates into the sky causing acid to form and resulting in easily detectable global cool spells - for instance the one following the eruption of Mount St Helens.

According to Professor Carl Percival, Criegee intermediates released naturally into the atmosphere by living ecosystems have a constant cooling effect which could be at least as big as that produced by volcanic eruptions. Last year, after the initial confirmation that at least one of the tricky chemicals existed and worked as described, he said:

"This new source of atmospheric sulphates is at least as important as the one we knew about already, and in some cases it can dominate."

Sulphur-based aerosols are already acknowledged by all sides in the climate debate as a major factor in climate modelling, so the added effect potentially produced by Criegee intermediates could mean a serious adjustment downwards for future climate forecasts.

However the actual effect to be assigned was highly uncertain, as nobody could say for sure how quickly the exotic chemicals would do their work. The state of play has now moved forward somewhat, however, as Percival and his fellow scientists have moved on to measure the effects of a second Criegee intermediate: namely CH3CHOO.

“One of the main questions from our first study was if this increased reactivity would be observed for other Criegee intermediates, so with these findings we now have additional evidence that Criegee intermediates are indeed powerful oxidisers of pollutants such as nitrogen dioxide and sulphur dioxide," explains Percival in a statement issued today by his university, Manchester.

“What this study suggests is that the biosphere could have a significant impact on aerosol production and thus potentially climate cooling via the formation of Criegee intermediates," he adds. "The next steps will be to carry out modelling studies to quantify the impact of Criegee intermediates on climate and to quantify the level of alkene present in various environments.”

As and when that work is completed, it might perhaps go some way towards explaining the generally flat global temperatures seen over the last decade and more, which are increasingly puzzling for those climate scientists who had expected them to keep going up at the rate they did between 1970 and the 1990s.

Percival and his colleagues' latest study is published by the journal Science, here. ®